Group B Strep in Pregnancy: Testing, Risks, and What Happens During Labour

Fact-Checked & Transparent: This article is fact-checked against current CDC, WHO, ACOG, and NHS guidelines. All health information is based on authoritative medical sources. Last verified: June 2026.

⚠️ MEDICAL DISCLAIMER

This article is educational information only. It is NOT a substitute for professional medical advice, diagnosis, or treatment.

Always consult your pediatrician or healthcare provider before making any medical decisions for your baby or child. Every baby is unique, and professional medical guidance is essential.

In case of emergency, call 911 or your local emergency number.

What Is Group B Streptococcus?

Group B Streptococcus (GBS) — also called Streptococcus agalactiae or Group B Strep — is a type of bacteria found naturally in the gut and lower genital tract of many healthy adults. It is not a sexually transmitted infection and does not cause symptoms in the vast majority of people who carry it. Most adults who carry GBS have no idea.

Estimates suggest that between 20 and 30% of adults carry GBS at any given time, according to the Group B Strep Support charity (the UK's leading GBS charity). Colonisation is intermittent — a person may carry the bacteria one month and not the next, which has significant implications for testing accuracy.

During pregnancy, the concern is not about harm to the mother. GBS rarely causes problems for healthy adults. The concern is what can happen if GBS is present in the vagina or rectum at the time of birth, and the baby passes through an area where the bacteria are present.

How GBS Is Transmitted to a Baby

Newborns are exposed to GBS during labour and delivery — through the birth canal, or in rare cases through the membranes before delivery. Most babies exposed to GBS do not become ill. The bacteria do not reliably cause infection in every newborn they come into contact with. However, in a small proportion of cases, GBS can cause a serious, rapidly progressing neonatal infection.

The risk of a baby being infected is higher in specific circumstances. Understanding these risk factors is central to the approach taken by UK and US healthcare systems.

Risk Factors for Passing GBS to a Baby

The following risk factors significantly increase the likelihood of a baby developing GBS disease if exposed during birth:

• Preterm labour (before 37 weeks): Preterm babies are more vulnerable because their immune systems are less mature.
• Prolonged rupture of membranes: If membranes rupture more than 18 hours before delivery, the baby has more prolonged exposure.
• Fever during labour: A temperature of 38°C or above in labour is a risk factor for GBS and for infection generally.
• A previous baby affected by GBS disease: A history of a previous baby with GBS disease is one of the strongest risk factors.
• GBS found in urine during this pregnancy: GBS bacteriuria indicates heavy colonisation and is an automatic trigger for antibiotics in labour in both UK and US guidance.
• Known GBS carrier status in this pregnancy (for women who have been tested).

The US Approach: Routine Testing at 35–37 Weeks

In the United States, the CDC and the American College of Obstetricians and Gynecologists (ACOG) recommend universal screening of all pregnant women for GBS between 35 and 37 weeks of pregnancy. The test involves a combined vaginal-rectal swab, which is sent to a laboratory.

If the swab comes back positive, the woman receives intravenous (IV) antibiotics during labour as a standard precaution, regardless of whether other risk factors are present.

The logic behind universal screening is straightforward: it identifies carriers in advance and allows a planned antibiotic protocol to be in place for labour. The limitation is that colonisation is intermittent — a woman who tests negative at 35 weeks may have acquired GBS by the time labour begins.

The UK Approach: Risk-Based Testing

The NHS in the UK does not offer routine antenatal GBS screening to all pregnant women. This is a deliberate policy decision, not an oversight. The National Screening Committee reviewed the evidence and concluded that universal screening does not reliably predict which babies will be at risk, due to the fluctuating nature of colonisation, and could lead to very high numbers of women receiving unnecessary antibiotics in labour.

Instead, the UK uses a risk-factor-based approach. Women are offered IV antibiotics in labour if they have one or more of the clinical risk factors listed above. GBS found incidentally — for example on a swab taken for another reason, or via a private test — is treated as a risk factor and triggers antibiotic offer.

Some UK organisations, including the Group B Strep Support charity, argue that routine testing should be offered. This remains an area of ongoing debate within UK obstetrics.

Private GBS Testing in the UK

Some women in the UK choose to have a private GBS swab test, available from organisations including the Group B Strep Support charity's testing programme. These are usually done at around 35–37 weeks. A positive result means a woman can inform her midwife and request IV antibiotics in labour.

It is worth knowing that a negative private swab result does not guarantee GBS-free status at the time of labour — colonisation can change. A negative result reduces the likelihood but does not eliminate risk. This should be part of the conversation when interpreting a negative test.

Antibiotics in Labour: What to Expect

The treatment for known or suspected GBS carrier status in labour is intravenous antibiotics. The first-line antibiotic is penicillin (benzylpenicillin), given through a cannula (a small needle in a vein). This is highly effective at reducing the amount of bacteria present as the baby passes through the birth canal.

For women with a penicillin allergy, alternative antibiotics including clindamycin or cefazolin may be used, depending on allergy severity. It is important to inform your midwife of any antibiotic allergies at your booking appointment.

Antibiotics need to be started at least 4 hours before delivery to provide optimal protection. This means that for women who are GBS positive or have risk factors, going to hospital early when labour begins is strongly advised — you should not wait until contractions are very frequent before heading in.

The antibiotics do not guarantee that the baby will not be exposed to GBS, but they substantially reduce the risk of the baby developing infection. NHS and ACOG guidance both support this approach as effective.

What GBS Disease Looks Like in Newborns

GBS infection in newborns is classified as either early-onset or late-onset.

Early-Onset GBS Disease

Early-onset disease develops within the first 7 days of life, and most commonly in the first 12–24 hours. It is the most common form of GBS disease in newborns and is the type that intrapartum antibiotics target.

Symptoms in the newborn include:

• Breathing difficulties or grunting
• Floppiness or unusual limpness
• Fever or abnormally low temperature
• Difficulty feeding or poor feeding
• High-pitched or unusual crying
• Pale, mottled, or bluish skin
• Seizures (in more severe cases)

These symptoms can develop very rapidly. If you notice any of these in your newborn — especially in the first 24 hours — seek medical attention immediately. This is a medical emergency.

Early-onset GBS can cause septicaemia (blood infection), pneumonia, and meningitis. Treated promptly with IV antibiotics, many babies recover fully. Outcomes are significantly worse when diagnosis is delayed.

Late-Onset GBS Disease

Late-onset GBS disease develops between 7 days and 3 months of life. It is less directly linked to labour and delivery and is not reliably prevented by intrapartum antibiotics. The source of infection in late-onset cases is often unclear — it may come from the environment, other people, or the mother's breast milk (though this is uncommon).

Symptoms are similar to early-onset disease. GBS meningitis is more commonly associated with late-onset disease and can cause long-term complications. Any newborn showing signs of serious illness in the first 3 months of life requires urgent medical assessment.

Outcomes With and Without Treatment

The Group B Strep Support charity estimates that approximately 1 in 1,750 babies born in the UK develops GBS disease. With prompt treatment, most survive. However, GBS remains the most common cause of life-threatening infection in newborns in the UK.

Without treatment, the outcomes of GBS disease are substantially worse — a small number of affected babies die, and some survivors have lasting disabilities including deafness, vision impairment, or neurological difficulties following meningitis.

The administration of intrapartum antibiotics to women with risk factors has been shown to significantly reduce the rate of early-onset GBS disease in newborns.

What GBS-Positive Women Should Do in Labour

If you are known to carry GBS, have had a previous baby with GBS disease, or have other risk factors, the following steps are important:

• Inform your midwife at the start of labour and at every handover of care.
• Go to the hospital or birth centre early when labour begins — do not delay, as antibiotics need at least 4 hours to work.
• Do not wait until contractions are 3–4 minutes apart if you carry GBS — get assessed sooner.
• If you have a home birth planned and carry GBS, discuss with your midwife how IV antibiotics will be administered and whether your home birth plan is still appropriate.
• After birth, make sure the neonatal team is informed of your GBS status so your baby can be monitored appropriately.

Breastfeeding and GBS

GBS status does not affect your ability to breastfeed. The NHS does not advise against breastfeeding for GBS-positive mothers. While GBS can occasionally be detected in breast milk, transmission of GBS disease via breast milk is rare and breastfeeding is not considered a significant risk factor for late-onset GBS in most cases.

Frequently Asked Questions

If I tested negative for GBS at 35 weeks, does that mean my baby is safe?

A negative swab at 35–37 weeks significantly reduces — but does not eliminate — the risk of GBS being present at the time of labour. GBS colonisation can change between the time of testing and delivery. Women with a negative swab but who develop risk factors during labour (fever, prolonged rupture of membranes, preterm labour) may still be offered antibiotics based on those risk factors.

Will I automatically be tested for GBS on the NHS?

Not unless you have risk factors or GBS is found incidentally on another swab or urine test. The NHS does not offer universal GBS screening. If you want a test, you can ask your midwife about the clinical risk-factor approach or access private testing. If GBS is found in any test during pregnancy, inform your midwife.

What if I go into labour very quickly and there is no time for antibiotics?

If there is insufficient time for IV antibiotics (less than 4 hours before delivery), your baby will be monitored more closely after birth for signs of GBS disease. The paediatric team should be informed. Monitoring typically involves observation for at least 12 hours and may include blood tests depending on symptoms and risk factors.

Can GBS cause problems for me as the pregnant woman?

In most cases, GBS colonisation causes no symptoms or problems for the pregnant woman. In rare cases, GBS can cause a urinary tract infection (UTI) in pregnancy, which is treated with oral antibiotics. If untreated, GBS UTI in pregnancy can contribute to preterm labour.

Does GBS go away on its own without treatment?

GBS colonisation does fluctuate naturally and may not be detectable at delivery even if positive during pregnancy. However, this is not predictable, which is why women with known carrier status are offered intrapartum antibiotics regardless of when testing was done.

Is GBS common in subsequent pregnancies if I had it before?

Women who were GBS-positive in a previous pregnancy have a higher likelihood of being positive in subsequent pregnancies, though this is not certain. Previous GBS carrier status is noted in your obstetric records and will be taken into account in future pregnancies.

Key Takeaways

• GBS is carried by approximately 20–30% of adults with no symptoms; the concern in pregnancy is the risk of passing the bacteria to the newborn during birth.
• The US offers routine GBS swabs to all women at 35–37 weeks; the UK uses a risk-factor-based approach rather than universal screening.
• IV penicillin during labour is highly effective at reducing early-onset GBS disease in newborns and is the standard first-line treatment.
• Going to hospital early in labour is essential for GBS-positive women — antibiotics need at least 4 hours before delivery to work effectively.
• Early-onset GBS disease develops within the first 24 hours of life; symptoms including breathing difficulty, floppiness, and fever require immediate medical attention.
• A negative GBS swab reduces but does not eliminate risk; women with clinical risk factors during labour are still offered antibiotics regardless of a previous negative result.

📋 SOURCES & FACT-CHECKING

This article is compiled and verified against these authoritative sources: - CDC (Centers for Disease Control & Prevention) - WHO (World Health Organization) - ACOG (American College of Obstetricians and Gynecologists) - NHS (National Health Service) - AAP (American Academy of Pediatrics)

Last verified: June 2026

Educational content only. Always consult your pediatrician for medical decisions.

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